1. Field of the Invention
The present invention generally relates to a sensor structure and method of fabricating the same.
2. Discussion of Related Art
Generally, in order to check chemical species that exists in a gas state is performed using chemical analyzing instruments such as a chromatography or a mass analyzer. Recently, such chemical analysis is possible to be performed using a mobile device, so that there is an increasing demand in checking in real-time and on the spot whether or not the air is contaminated, the food quality is well managed, the virus is infected, and the chemical, biological and radiological substance is contaminated. In this respect, there has been an effort to make the existing chemical analysis device smaller.
However, such analysis instruments have a limitation so that, recently, a mobile analysis device has been progressively developed using a small chemical sensor. In particular, an electronic nose device has been progressively developed using a sensor array comprising a number of chemical sensors in order to detect various chemical species, contrary to the characteristics of the existing single sensor with which only a specific chemical species is detected.
As a sensor technology mainly used in the electronic nose system, there are a metal-oxide-semiconductor sensor represented with SnO2, a quartz crystal microbalance (QCM) device using a bulk acoustic, a surface acoustic wave (SAW) device using a surface acoustic, a conducting polymer device, a polymer composite device comprising a conductive particle and a non-conductive polymer, and a colorimetric technology using an absorption wavelength change of a single molecule.
Among these various sensor technologies, the conducting polymer and the polymer composite technologies have a merit in that it is capable of making various sensors easily to fabricate the sensor array for electronic nose system. However, since such sensor materials generally show a characteristic sensitive to the temperature and moisture, there is a problem that the temperature and the moisture should remain constant.
A chemical sensor fabricated with the prior art will now be described with reference to FIG. 1.
A chemical sensor in FIG. 1 has a structure that a detecting electrode 11 and a sensing layer 12 are formed on the front side and a heater line 13 and an underlying protective layer 14 are formed on the back side.
Although a polymer composite and a conducting polymer sensors using an organic polymer can operate at room temperature, since the detecting characteristics vary according to the temperature, a constant temperature condition should be met in order to obtain the constant detecting pattern. Generally, by keeping the temperature constantly at more or less 40° C., a measurement error due to the change of the external temperature can be minimized. However, the conventional chemical sensor has a significant heat loss to the outside, so that there existed a problem that there was too much power consumption to make a very small electronic nose device requiring the temperature control.
Further, since a physiochemical interaction between the detected chemical species and the sensor material varies according to the temperature of a sensor substrate, the detecting pattern of the sensor array is also changed, and experimental parameters relevant to the interaction can be derived by the measurement of the change of the detecting response according to the temperature. (Schierbaum et al, Sensors and Actuators A, 1992, 31, 130). This result is also disclosed in the preceding research (U.S. Pat. No. 5,911,872).
However, in order to perform the temperature-dependent measurement with the conventional substrate, it take more than 10 minutes to stabilize the temperature, so that a lot of power is consumed for very small portable electronic nose device and a lot of gases are required in stabilizing the sensor to make it difficult to substantially implement.